1. Field of the Invention
The present invention relates to a solid-state imaging apparatus, a driving method of the solid-state imaging apparatus and an electronic equipment.
2. Description of the Related Art
An imaging apparatus, such as a digital still camera, to convert light into an electric signal and to output an image signal includes a solid-state imaging apparatus as an image capture section (photoelectric conversion section). In the field of the solid-state imaging apparatus, in recent years, as the number of pixels is increased and a frame rate is raised, a technology of realizing high-speed reading and a technology of realizing low power consumption become essential technologies.
As a type of solid-state imaging apparatus, there is a CMOS (including a MOS) image sensor (hereinafter referred to as “CMOS image sensor”) taking advantage of a feature that it can be manufactured by the same process as a CMOS integrated circuit. The CMOS image sensor adopts such a structure that an electric charge is converted into an electric signal for each pixel, and the electric signals read from the pixels are processed in parallel for respective pixel columns. The readout rate of the pixel signals can be increased by the parallel processing for the respective pixel columns.
Hitherto, as a CMOS image sensor to read out signals in parallel for respective pixel columns from plural pixels arranged in a matrix form, there is known a column AD conversion type one which performs analog-to-digital conversion (hereinafter referred to as “AD conversion”) of pixel signals for the respective pixel columns (JP-A-2005-278135 (Patent document 1)).
The column AD conversion type CMOS image sensor adopts such a structure that signal readout lines (hereinafter referred to as “vertical signal lines”) are shared in the vertical direction of pixels two-dimensionally arranged in a matrix form, and an AD conversion circuit and a readout circuit are provided for each of the pixel columns. Then, the AD conversion circuits and the readout circuits are simultaneously driven, so that the simultaneous signal processing equivalent to the total number of pixel columns is performed.
The AD conversion circuit compares an analog pixel signal given through the vertical signal line with a reference signal of a linearly changing slope waveform having an inclination for each pixel column by a comparator, and starts a count operation of a counter. The counter performs the count operation in synchronization with a clock of a constant period.
Thereafter, the AD conversion circuit stops the count operation of the counter at the inverting timing of the output of the comparator when the analog pixel signal intersects with the reference signal. The final count value of the counter becomes the digital signal corresponding to the magnitude of the analog pixel signal. As described above, the column AD conversion system is a readout system characterized by high-speed image pickup since the pixel signals of one row are simultaneously A/D converted.